The use of cables, bars, strands and other types of tendons to effect prestressing of concrete members is a common practice in the construction industry today. More particularly, post-tensioning of concrete slabs, walls and beams by means of such tendons has gained wide acceptance. Such post-tensioning commonly employs at least one and usually two tendon gripping anchorages formed to secure the reinforcing tendon and hold the same under extremely high axial loads.
Numerous types of concrete prestressing anchorages have been evolved with each having certain advantages, depending upon the application to which they are put. One type of anchorage which has gained particularly widespread use is the cast-in-place anchorage which is normally employed to secure a single reinforcing tendon. These cast-in-place tendons are commonly used in the construction of floor slabs and tilt-up walls, and usually a substantial quantity of tendon anchorages is required in the construction a building. Accordingly, a primary consideration in the selection of cast-in-place anchorages is the cost of the anchorage and the cost of its installation. Many of the cast-in-place single strand anchorages employed today are sold at a price of about $1.25 to $1.75, and a price difference of $0.10 can be determinative of which anchorage will be used.
As a result of this very competitive pricing, many of the most economical concrete prestressing anchorages are formed by casting, which eliminates the cost involved in more expensive fabricating processes, such as machining, notwithstanding the inherent loss in reliability and reproducibility which a casting process produces. Similarly, the cost in terms of apparatus for mounting the anchorage, usually in a recessed position to the form board, should be minimal. Accordingly, these anchorages have employed nails and simple plastic re-usable pipes together with rubber or wooden block-out members to effect mounting while keeping costs down.
Some typical examples of single strand concrete prestressing anchorages which have been employed for securement of reinforcing tendons are set forth in the following U.S. Pats: 3,293,811; 3,399,434; 3,408,783; 3,605,361; 3,676,031 and 3,685,934. While the anchorage and method of the present invention are particularly well suited for construction of a cast-in-place type of anchorage as set forth in the above-referenced patents, because of the inherent low cost, it will be understood that the concrete anchorage of the present invention may have numerous other applications, including multiple strand anchorages, non-recessed installations, etc.
Accordingly, it is an object of the present invention to provide a method for forming an anchor member for use in a concrete prestressing anchorage which may be used to produce a very low cost anchorage having the high strength and reliability of machined anchorages.
It is another object of the present invention to provide a method for forming an anchor member for use in concrete prestressing anchorages which provides greater flexibility in the construction of the anchor member to accommodate a wider variety of installation conditions.
It is still a further object of the present invention to provide a method for forming an anchor member for use in a concrete prestressing anchorage which can be employed to provide the necessary structure for a variety of different anchorage mounting techniques.
Another object of the present invention is to provide an anchor member which is relatively inexpensive to construct and yet has high strength and reliability.